Ch 5 - EDX Neuromuscular Anatomy/Physiology Flashcards
Where is the cell body of a motor neuron located?
Anterior horn of the SC
Where is the cell body of a sensory neuron?
Located in dorsal root ganglion outside the SC in intervertebral foramen
What is an axon?
Projection from sensory or motor neurons that propagate current flow and transport nutrition
Where do axons of motor neurons project?
projects axons distal
Where do axons of a sensory neuron project?
Bipolar cells with 2 axons
1 projects proximal and one distal
What is the innervation ratio?
Amount of muscle fibers innervated by one axon
What is the innervation ratio of a muscles of gross movement?
High
The higher the ratio the higher the force
ex: 600 muscle fibers to one axon in leg
What is a myotome?
Group of muscles innervated by one spinal segement
What is a dermatome?
Sensory innervation of one spinal segment
What is a NMJ?
Sites where electric impulse along an axon converts to a chemical rxn and translated to an electrical impulse at postsynaptic mem to initiate a muscle fiber action potential (AP)
What is a motor unit?
Anterior horn cell Motor nerve axon Peripheral nerve NMJ Muscle fibers
What is the Henneman size principle?
Smaller alpha motor neuron has low threshold for excitation and is recruited first in voluntary contraction
(Large recruited for greater contractile force)
Describe Type I muscle fibers
Small cell body
Thin diameter axon
Low innervation ratio
Slow twitch muscle fibers
Describe Type II muscle fibers
Large cell body
Thick diameter axon
High innervation ratio
Fast twitch muscle fibers
What type of fibers does EDX evaluate?
Ia (large, myelinated) fibers
What does the cathode of EDX do?
Neg cathode attracts positive charges and lowers membrane potential allowing Na to rush through voltage-gated channels and generate an AP
How do cooler temperatures impact EDX?
Prolongs latency
Inc: amp, duration
Dec: CV
What is saltatory conduction?
Propogation of current between myelin in Na channels in nodes of Ranvier
What is orthodromic recording?
AP recorded in direction of physiologic conduction
What is antidromic recording?
AP recorded in opposite direction of physiologic conduction
How is a miniature endplate potential (MEPP) created?
Spontaneous release of Ach ~ 5 sec during resting state at NMJ
How is an endplate potential (EPP) produced?
Nerve depolarization opens voltage-gated Ca channels and release Ach into synaptic cleft which inc # of MEPP and generates a MUAP
Describe a Type I muscle fiber
Small Dark Early recruitment Highly resistant to fatigue Mild effort (4-8 hz) Slow, prolonged firing freq Fine, precise movements Small innervation ratio Small amp/duration Aerobic
Describe a Type IIA muscle fiber
Large Dark Late recruitment Fatigue resistant Intermed effort (20-30 Hz) Fast, unsustained firing freq Gross movements Large innervation ratio Large amp/duration Anaerobic
Describe a Type IIB muscle fiber
Fast Twitch Glycolytic Large Pale Late recruitment Fatigue sensitive High effort (20-30 Hz) Fast, unsustained firing freq Gross movements Large innervation ratio Large amp/duration Anaerobic
What is Endoneurium?
CT surrounding each individual axon and its myelin sheath
What is Perineurium?
CT surrounding bundles or fascicles of myelinated and unmyelinated nerve fibers
What is Epineurium?
Loose CT surrounding entire nerve that holds fascicles together and protects from compression
What does the needle EMG monitor?
Factors related to the motor unit and thus the alpha motor neuron
